Gas turbine engines are made to operate more efficiently by increasing the turbine operating temperatures to very high levels. Since the preferred temperatures are well above the temperatures allowable for use with current flow path metals, it is necessary to provide cooling of these parts in order that they may exhibit acceptable life characteristics. The turbine blades which operate in the main gas flow stream can be cooled among others by way of impingement cooling. The tip seal which surrounds the row of turbine blades forming a stationary outer flow path is usually cooled by way of impinging a supply of cooling air to flow directly on the outer surface of the tip seal element. Traditionally, impingement of air against the outer surface of the tip seal is accomplished by way of an impingement baffle which is mounted to the outer surface of the tip seal structure.
It is an aim of gas turbine engines to have a high efficiency and among other things a long tip seal life. Therefore, it is desired to provide an efficient cooling of turbine tip seal segments. To obtain good cooling the impingement baffle, comprising normally an impingement plate or an impingement ring, should not crack and should not wear. Therefore, the arrangement of an impingement plate or an impingement ring is very important. For example, wear may be caused by impingement rings which are inadequately fastened or which are translated circumferentially during operation in a cavity between tip seals and a carrier ring. High stresses in impingement plates or rings can cause cracks.
It is known to use separate impingement plates which are usually brazed together. Further, impingement rings are known which are made of more than one part. The fixing of separate impingement plates or of parts of an impingement ring is difficult, complex and cost-intensive because of the time required for fixing. Furthermore, continuous impingement rings are known. Continuous impingement rings or closed impingement rings, respectively, have the disadvantage that they can cause high stresses and therefore the continuous impingement rings have a high cracking risk.
The impingement plates and impingement rings should be arranged to avoid wear of mating surface on tip seals. Therefore, impingement plates or impingement rings are advantageously arranged tangential to the tip seal elements.